This application addresses broad Challenge Area 11, entitled Regenerative Medicine. The specific Challenge Topic is 11-DC-101, Hair Cell Regeneration and Maintenance. Deafness and lesser degrees of hearing impairment have an enormous impact on modern societies. Throughout the industrialized world, about one-tenth of the population suffers from functionally significant hearing and balance problems. The societal impact of hearing loss is immense. In addition to its annual cost in the United States of more than $80 billion, hearing disease delays the acquisition of speech in infants, isolates the elderly, and depresses affected individuals of all ages. A promising avenue to the alleviation of deafness is the restoration of normal hearing by regeneration of hair cells in the human cochlea. We wish to determine the particular genes whose activation underlies the renewal of hair cells in species whose receptors normally turn over. In particular, we hope to investigate the lateral-line organ of the larval zebrafish, a preparation in which hair-cell regeneration has been described in detail. We shall begin by ascertaining which molecular signals are activated by hair-cell death, the stimulus for regeneration. We next plan to determine the particular signaling pathways that are activated when quiescent stem cells and amplifying progenitors transition to their mitotically active states. Finally, we intend to understand what pathways are upregulated as immature cells differentiate into functional hair cells. The structure, development, and operation of hair cells are conserved throughout the vertebrates. We accordingly anticipate that a detailed understanding of the molecular events underlying hair-cell regeneration in a model system will be useful in restoring human hearing. Identifying the changes in gene expression by stem cells and hair-cell progenitors will provide clues about the signaling pathways that are activated at the outset of hair-cell regeneration. Because pharmacological manipulation of the relevant molecular signals may restore the activity of stem cells in the mammalian inner ear, these pathways constitute logical targets for therapeutic approaches to the regeneration of hair cells in the human cochlea and vestibular apparatus. Gene-expression patterns during hair-cell regeneration PUBLIC HEALTH RELEVANCE: Deafness and lesser degrees of hearing impairment have an enormous impact on modern societies: about one-tenth of our population suffers from functionally significant hearing and balance problems. A promising avenue to the alleviation of deafness is the restoration of normal hearing by regeneration of hair cells in the human cochlea. We wish to determine the signaling pathways that underlie the renewal of hair cells, for these pathways constitute logical targets for therapeutic approaches to the regeneration of hair cells in the human cochlea and vestibular apparatus.